Geode

A hollow, roughly spherical rock cavity lined with crystals (quartz, amethyst, calcite) that grew inward from the walls; formed in gas bubbles in lava or in dissolved concretions in sediment. Cut or cracked open to display.

Sources

Earle, S. (2019). Physical Geology, 2nd ed., Chapter 2: Minerals (CC BY 4.0)
Mindat — Mineralogical glossary (link only)

Cite this article

Stratum Study. "Geode" (Glossary). Stratum Study pack 2026.09, as of 2026-09-16. https://stratum.black/study/glossary/geode. Accessed 2026-09-20.

BibTeX · CSL-JSON

@misc{stratum-geode,
  title        = {Geode},
  author       = {{Stratum Study}},
  howpublished = {\url{https://stratum.black/study/glossary/geode}},
  year         = {2026},
  note         = {Glossary article, Stratum Study pack 2026.09, as of 2026-09-16; sources: stratum. Accessed 2026-09-20.}
}

Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.